1. Technical Field
The present invention relates to a clear ink composition used for ink jet recording methods. More specifically, the present invention relates to an ink composition for ink jet recording which is capable of forming high-quality records having excellent fixability and no printing spot on various recording media, particularly recording media with low water absorption, such as synthetic paper, printing paper for running-on, and the like.
2. Related Art
An ink jet recording method is a printing method in which ink droplets are scattered and allowed to adhere to a recording medium such as paper or the like. In recent years, innovative advance of ink jet recording techniques has made it possible to use an ink jet recording method in the field of high-definition printing which has been realized only by silver salt photography and offset printing. This trend has led to the development of inks for ink jet recording capable of realizing images having glossy impression comparable to that of silver salt photographs using, for ink jet recording, recording media with high glossiness comparable to printing paper, art paper, and the like which have been used in the field of silver salt photography and offset printing, i.e., specialty paper. Also, there has been developed inks for jet recording capable of realizing image quality comparable to silver salt photographs even by using plain paper.
In order to realize high image quality, it has been proposed to record by adhering an ink composition and a clear composition not containing a colorant to a recording medium. For example, Japanese Unexamined Patent Application Publication No. 2003-335058 has proposed that an image is formed using an ink composition containing a colorant, and a clear ink composition is adhered to the image.
In particular, in the printing field, desktop publishing (DTP) having been popularized with recent popularization of a technique of forming images from digital data. Even in printing by DTP, color proof is previously formed for confirming the glossy impression and color impression of actual prints. An ink jet recording system is applied to output of the proof. Since DTP requires color reproduction and stability reproduction of prints, specialty paper for ink jet recording is generally used as a recording medium.
Specialty paper for ink jet recording is prepared so as to exhibit the same glossy impression and color impression as those of an output obtained by actually printing on printing paper for running-on. Although the material of specialty paper is appropriately controlled according to the type of printing paper for running-on, the production of specialty paper matching with all of a variety of printing paper for running-on increases the production cost. Therefore, in application to color proof, it is desired to perform ink jet recording on printing paper for running-on rater than specialty paper. Also, it is considered that if printed matter produced by ink jet recording directly on printing paper for running-on can be used as a final proof sample without use of specialty paper, the cost required for proof can be significantly decreased. In addition, synthetic paper, which is widely used in printing fields and prepared by forming into a film a mixture of polyethylene resin, polyester resin, an inorganic filler, and the like, has excellent recycling properties and has recently attracted attention as an environment-friendly material.
Printing paper for running-on is coated paper including a coating layer provided on a surface thereof for receiving oil-based ink, but has a characteristic that the coating layer has a low ink absorbing ability. Therefore, when water-based pigment ink, which is generally used for ink jet recording, is used, bleeding or uneven coagulation may occur in an image due to low ink penetrability into a recording medium (printing paper for running-on).
With respect to this problem, for example, Japanese Unexamined Patent Application Publication No. 2005-194500 discloses a pigment-based ink having improved blurring and excellent glossiness for specialty paper and containing a polysiloxane compound as a surfactant and an alkanediol such as 1,2-hexanediol as a dissolution aid. Japanese Unexamined Patent Application Publication Nos. 2003-213179, 2003-253167, and 2006-249429 have proposed that diol such as glycerin, 1,3-butanediol, or the like, or a triol alcohol solvent such as pentaerythritol or the like is added to ink, for controlling penetrability of the ink to a recording medium, thereby forming high-quality images.